The truth about sports, nutrition and pain!

Posts tagged ‘marathons’

¨Hitting the wall¨

You probably have heard of this expression before if you are a runner and may have even experienced it yourself. ¨Hitting the wall¨ usually happens around the 29th to 35th kilometer. The runner´s pace slows down considerably, the legs become very heavy and thinking often becomes hard and confused (now that I think about it, this last thing happens to me quite often). This happens because we basically run out of available energy.

The runner´s primary sources of energy during prolonged exercise are carbohydrates and fats. We have lots of stores of fat, around 70.000 to 75.000 kcla, even in a lean adult, but the fat metabolism requires a constant supply of oxygen, and delivery of energy is slower than that provided by the carbohydrate metabolism. The carbs reserves (glycogen), on the other hand, are quite limited and have only around 2.000 to 2.400 kcla, which happens to be enough energy to get us to kilometer 29-30. Since the body is much less efficient at converting fat to energy, running pace slows and the runner suffers from fatigue.To make things even worse the brain, which  only accounts for 2% of your weight and consumes 20% of your energy, gets its fuel source only from carbohydrates!!  So now next you ¨hit the wall¨you will know why that is. Hope you liked it. Till next time


Kenney L, Wilmore J, Costill D. Physiology of Sport and Exercise sixth edition, Human Kinetics,2015.

Why do we get muscle cramps while training part 2

As I mentioned in my last post, scientist still don’t know why we get muscle cramps while exercising. The old theory was the electrolyte depletion and the new one is the muscle fatigue. I gave some flaws of the electrolyte theory, but this does not mean that I totally disregard that theory. As there are some people who actually lose salt at a rate five times faster than normal. Salts are essential to hydration despite of that mineral’s reputation for drying you out.  A body short of salts won’t deliver the water efficiently to the muscles. So even if you are drinking bottles and bottles of water, nothing will happen. The thing is that most people don’t lose salt so fast so, in my opinion, most of the exercise muscle cramps come from fatigue. There is also a difference between electrolyte depletion cramps and fatigue cramps. Electrolyte depletion cramps are much more serious, they affect more than one muscle and stretching won’t alleviate the cramp. Fatigue related cramps aren’t that serious, and usually by stopping the activity and stretching the cramp will go away.

So what can we do to try to avoid the muscle fatigue cramps? Go slower, decrease the intensity or train better, let me explain. We often get these cramps in competition and not while training. This is usually because, when we are competing, we are going faster or more intense than during practice due to the adrenaline or to due the mere fact that we are competing to get the best results. If the body is not trained to go at that intensity it will get tired faster, meaning a higher chance of getting a cramp.  And that is what the studies have shown, namely that the increased running speed is what predicts who will get the exercise associated muscle cramps. (1-5)

Hope you liked it.

  1. Schwellnus MP, Drew N, Collins M: Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: a prospective cohort study in 210 Ironman triathletes. Br J Sports Med, 1-7, Dec. 9, 2010
  2. Schwellnus MP, Derman EW, Noakes TD. Aetiology of skeletal muscle cramps during exercise: A novel hypothesis. Journal of Sports Sciences, vol.15, pp 277-85. 1997
  3. Schwellnus MP. Muscle cramping in the marathon:aetiology and risk factors. Sports medicine. Auckland, NZ 2007.
  4. Schwellnus MP. Cause of exercise associated muscle cramps ( EAMC)–altered neuromuscular control, dehydration or electrolte depletion?
  5. Braulick KW, Miller KC, Albrecht JM, Tucker JM, Deal JE. Significan and serious dehydration does not affect skeletal muscle cramp threshold frequency. Br J Sports Med, 1009 Jun:43(6):401-8

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